Various types of medical electrical leads for use in cardiac rhythm management (CRM) and neurostimulation applications are known. In CRM applications, for example, such leads are frequently delivered intravascularly to an implantation location on or within a patient's heart, typically under the aid of fluoroscopy. Once implanted, the lead is coupled to a pulse generator or other implantable device for sensing cardiac electrical activity, delivering therapeutic stimuli, and/or for performing some other desired function within the body. Such leads often include a distal, conductor section which contacts the heart tissue, and a proximal, terminal section which is connected to a pulse generator. The distal section of the lead can include a number of ring-shaped electrodes that supply electrical currents to adjacent heart tissue for pacing the heart and/or for sensing heart function. The electrodes are typically attached to a conductor cable or coil within the interior of the lead via a welded, crimped, and/or staked connection joint.
In some lead designs, the distal section of the lead may have a pre-biased shape that is used to secure the lead within the body. In certain lead configurations, for example, the implantable lead can have a helical or S-shaped distal section that serves to secure the lead to the walls of a vein or artery. When implanted within the body, the electrodes may have an inactive portion that does not contact adjacent target tissue, but which affects the current density around the surface of the electrode. Furthermore, in some cases the inactive portion of the electrode can direct current toward an undesired stimulation site such as the phrenic nerve in CRM applications. In some cases, the inactive portion of the electrode not in contact with the target tissue can decrease the amplitude of the current density at the active (i.e., target) region of the electrode, reducing the overall efficiency of the electrode in providing electrical stimulus and/or to sense cardiac electrical activity. For ring-type electrodes having a uniform wall thickness throughout, for example, the electrodes often include one or more inactive portions that are not in contact with the adjacent target body tissue, but which affect the magnitude and directionality of the current density.